Moved issuer-index.html from CSOL theme to main admin view dir.

There was nothing CSOL-specific about the page, so we might as well move
it.
Allow issuers to manage claim codes.

Fixes #219.

This is a kind of odd solution to the problem, because it duplicates all the
claim-related endpoints under the `/admin/` path to the `/issue/` path,
rather than e.g. changing the auth privileges required to access only one
set of claim-related endpoints.
Merge pull request #221 from toolness/issue-219-issuer-claim-codes

Allow issuers to manage claim codes.